K complex
A K-complex is an electroencephalography (EEG) waveform that occurs during stage 2 of NREM sleep. It is the "largest event in healthy human EEG".Cash, S.S.; Halgren, E.; Dehghani, N.; et al. (2009). Human K-Complex Represents an Isolated Cortical Down-State. Science, 324:1084–87 PMID 19461004 They are more frequent in the first sleep cycles. K-complexes have two proposed functions: first, suppressing cortical arousal in response to stimuli that the sleeping brain evaluates not to signal danger, and second, aiding sleep-based memory consolidation. The K-complex was discovered in 1937 in the private laboratories of Alfred Lee Loomis.Loomis, A.L.; Harvey, E.N.; Hobart, G.A. (1937). Cerebral states during sleep as studies by human brain potentials. J Exp Psychol, 21:127–44.abstract Neurophysiology K-complex consists of a brief negative high-voltage peak, usually greater than 100 µV, followed by a slower positive complex around 350 and 550 ms and at 900 ms a final negative peak. K-complexes occur roughly every 1.0–1.7 minutes and are often followed by bursts of sleep spindles. They occur spontaneously but also occur in response to external stimuli such as sounds, touches on the skinRoth, M.; Shaw, J.; Green, J. (1956). The form, voltage distribution and physiological significance of the K-complex. Electroenceph Clin Neurophysiol 8:385–402. PMID 13330651 and internal ones such as inspiratory interruptions.Webster, K.E.; Colrain, I.M. (1998). Multichannel EEG analysis of respiratory evoked-potential components during wakefulness and NREM sleep. J Appl Physiol 85:1727–35. They are generated in widespread cortical locations though they tend to predominate over the frontal parts of the brain.McCormick L, Nielsen T, Nicolas A, Ptito M, Montplaisir J. (1997). Topographical distribution of spindles and K-complexes in normal subjects. Sleep. 20(11):939-41. PMID 9456457 Both K-complex and delta wave activity in stage 2 sleep create slow-wave (0.8 Hz) and delta (1.6–4.0 Hz) oscillations. However, their topographical distribution is different, and the delta power of K-complexes is higher.Happe, S.; Anderer, P.; Gruber, G.; Klösch, G.; Saletu, B.; Zeitlhofer, J. (2002). Scalp topography of the spontaneous K-complex and of delta-waves in human sleep. Brain Topogr. 15(1):43–9. PMID 12371676 They are created by the occurrence in widespread cortical areas of outward dendritic currents from the middle (III) to the upper (I) layers of the cerebral cortex. This is accompanied by a decrease in broadband EEG power including gamma wave activity. This produces "down-states" of neuronal silence in which neural network activity is reduced. The activity of K-complexes is transferred to the thalamus where it synchronizes the thalamocortical network during sleep, producing sleep oscillations such as spindles and delta waves.Amzica, F.; Steriade, M. (1998). Cellular substrates and laminar profile of sleep K-complex. Neuroscience. 82(3):671–86. PMID 9483527 It has been observed that they are indeed identical in the "laminar distributions of transmembrane currents" to the slow waves of slow-wave sleep. K-complexes have been suggested both to protect sleep and also to engage in information processing, as they are both an essential part of the synchronization of NREM sleep, while they also respond to both internal and external stimuli in a reactive manner.Halász, P. (2005). K-complex, a reactive EEG graphoelement of NREM sleep: an old chap in a new garment. Sleep Med Rev. 9(5):391–412. PMID 16122950 This would be consistent with a function in suppressing cortical arousal in response to stimuli that the brain needs to initially process in regard to whether it is dangerous or not. Another suggested function is aiding the activation homeostasis of synapsesTononi, G.; Cirelli, C. (2006). Sleep function and synaptic homeostasis. Sleep Med Rev. 10(1):49–62. PMID 1637659 and memory consolidation. The activation thresholds of cortical synapses become lowered during wakefulness as they process information, making them more responsive, and so need to be adjusted back to preserve their signal-to-noise ratio. The down-state provided by K-complexes does this by reducing the strengths of synaptic connections that occur while an individual is awake. Further, the recovery from the down-state they induce allows that "cortical firing 'reboots' in a systematic order" so that memory engrams encoded during neuronal firing can be "repeatedly practiced and thus consolidated". Development They are present in the sleep of 5-month-old infants, and develop with age. Between 3 and 5 years of age a faster negative component appears and continues to increase until adolescence. Another change occurs in adults: before 30 years of age their frequency and amplitude is higher than in older people particularly those over 50 years of age.Wauquier, A. (1993). Aging and changes in phasic events during sleep. Physiol Behav 54:803–6. PMID 8248360 This parallels the decrease in other components of sleep such as sleep spindle density and delta power. Clinical Epilepsy In individuals with idiopathic generalized epilepsy, K-complex induced synchronization can trigger spike-and-wave discharges. This tends to happen most between the shift between waking and NREM, and between NREM and REM sleep.Steriade, M.; Amzica, F. (1998). Slow sleep oscillation, rhythmic K-complexes, and their paroxysmal developments. J Sleep Res. 7 Suppl 1:30–5. PMID 9682191 In autosomal dominant nocturnal frontal lobe epilepsy, K-complexes are almost invariably present at the start of seizures.El Helou, J.; Navarro, V.; Depienne, C.; Fedirko, E.; LeGuern, E.; Baulac, M.; An-Gourfinkel, I.; Adam, C. (2008). K-complex-induced seizures in autosomal dominant nocturnal frontal lobe epilepsy.Clin Neurophysiol. 119(10):2201–4. PMID 18762450 Restless legs syndrome Individuals with restless legs syndrome have increased numbers of K-complexes and these are associated with (and often precede) leg movements. Dopamine enhancing drugs such as L-DOPA that reduce leg movements do not reduce the K-complex suggesting that they are primary and the leg movements secondary to them. Failure of such drugs to reduce K-complexes in spite of reducing the leg movements has been suggested to be why patients after such treatment still continue to complain of non-restorative sleep.Montplaisir, J.; Boucher, S.; Gosselin, A.; Poirier, G.; Lavigne, G. (1996). Persistence of repetitive EEG arousals (K-alpha complexes) in RLS patients treated with L-DOPA. Sleep. 19(3):196–9. PMID 8723375 Clonazepam is another treatment for RLS; like other benzodiazepines, it inhibits REM sleep by enhancing levels of GABA. This inhibition of REM sleep significantly decreases K-complex count, and unlike L-DOPA treatment, clonazepam studies report improvement in sleep restoration.Saletu, M. (2001). Restless legs syndrome (RLS) and periodic limb movement disorder (PLMD) acute placebo-controlled sleep laboratory studies with clonazepam. European Neuropsychopharmacology, 11(2):153–161 Therefore, drugs that inhibit REM sleep also decrease K-complex count. Obstructive sleep apnea Obstructive sleep apnea syndrome is associated with inspiratory occlusions evoking fewer K-complexes during NREM sleep even though K-complexes are evoked normally to auditory stimuli and such individuals react normally to respiratory interruptions when awake. This suggests a link between such sleep apnea and a sleep specific blunted cortical response to respiratory problems.Huang, J.; Colrain, I.M.; Melendres, M.C.; Karamessinis, L.R.; Pepe, M.E.; Samuel, J.M.; Abi-Raad, R.F.; Trescher, W.H.; Marcus, C.L. (2008). http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=2276751&blobtype=pdf Cortical processing of respiratory afferent stimuli during sleep in children with the obstructive sleep apnea syndrome]. Sleep. 31(3):403–10. PMID 18363317Gora, J.; Trinder, J.; Pierce, R.; Colrain, I.M. (2002).Evidence of a sleep-specific blunted cortical response to inspiratory occlusions in mild obstructive sleep apnea syndrome. Am J Respir Crit Care Med. 166(9):1225–34. PMID 12403692Afifi, L.; Guilleminault, C.; Colrain, I.M. (2003). Sleep and respiratory stimulus specific dampening of cortical responsiveness in OSAS. Respir Physiol Neurobiol. 136(2–3):221–34. PMID 128530 Notes Category:Sleep Category:Electroencephalography Category:Sleep_physiology